1. Field of the Invention
The present invention relates generally to probe cards that are used to perform tests on semiconductor devices. The present invention more particularly relates to the cleaning of probe elements that extend from such probe cards.
2. Background Art
Individual semiconductor (integrated circuit) devices (dies) are typically produced by creating several identical dies on a semiconductor wafer, using known techniques of photolithography, deposition, and the like. Generally, these processes are intended to create a plurality of fully-functional integrated circuit devices, prior to singulating (severing) the individual dies from the semiconductor wafer. In practice, however, certain physical defects in the wafer itself and certain defects in the processing of the wafer inevitably lead to some of the dies being xe2x80x9cgoodxe2x80x9d (fully-functional) and some of the dies being xe2x80x9cbadxe2x80x9d (non-functional). It is generally desirable to be able to identify which of the plurality of dies on a wafer are good dies prior to their packaging, and preferably prior to their being singulated from the wafer. To this end, a wafer xe2x80x9ctesterxe2x80x9d or xe2x80x9cproberxe2x80x9d may advantageously be employed to make a plurality of discrete pressure connections to a like plurality of discrete connection pads (bond or contact pads) on the dies. In this manner, the semiconductor dies can be tested and exercised, prior to singulating the dies from the wafer. A conventional component of a wafer tester is a xe2x80x9cprobe cardxe2x80x9d to which a plurality of probe elements are connectedxe2x80x94tips of the probe elements effecting the pressure connections to the respective pads of the semiconductor dies.
More specifically, in the typical wafer testing process, the probe card is mounted to the prober, and probe elements (simply referred to as xe2x80x9cprobesxe2x80x9d) extending from the probe card are brought into contact with pads formed on the dies of the wafer. In one process, electrical connection of the prober and the pads is achieved by applying a predetermined pressure to the probes after the probes have been brought into contact with the pads so that the probes penetrate the material forming the surface of the pads and come into low-resistance contact with the portions forming the bodies of the pads. Such penetration of the pad surfaces produces debris (e.g., aluminum oxide chips). In a more preferred process, used with probes that are elastic or springy, electrical connection of the prober and the pads can be achieved by applying a predetermined pressure to the springy probes after the probes have been brought in contact with the pads so that the probes are compressed, making a solid electrical connection. When the probes are compressed, a slight X and/or Y swipe is affected to the probes causing a portion of the material (e.g., an aluminum oxide film) forming the surface of the pads to be scraped off. The scraping of the pad surfaces produces debris (e.g., aluminum oxide chips).
Foreign matter including aluminum oxide chips (i.e., debris) adhering to the dies and/or the probes may obstruct proper electrical connection. Various measures have been taken to prevent problems in achieving satisfactory electrical contact.
In one conventional probe cleaning process, an abrading pad is used to remove foreign materials adhering to end portions (e.g., tips) of the probes. The abrading pad can be composed of a mixture of an elastic base material and abrasive particles. Alternatively, the abrading pad can be composed of tungsten carbide. Foreign materials adhering to the tips of the probes are scraped off the tips by repeating a cleaning cycle of pressing-and-extracting the tips of the probes against (and possibly into) the pad. The pressing-and-extracting cleaning cycle includes moving the abrading pad vertically (e.g., in the Z direction) against the probes, and then vertically away from the probes.
A disadvantage of the above described conventional cleaning process is that the portions of the base material (e.g., silicon rubber) and/or abrasive particles (e.g., abrasive grains) may fall or chip off the abrading pad during the pressing-and-extracting process, thereby producing additional foreign material that may stick to the probe tips. Further, foreign matter (previously removed from probe) that has fallen onto the abrading pad may later stick to the probes being cleaned. Accordingly, additional cleaning steps may be necessary to acceptably clean the probes.
These additional steps may include blowing an organic solvent against the probes, and then blowing dry air against the probes. The use of such solvents is undesirable for many reasons. For example, the blowing of an organic solvent is time consuming and potentially messy. Additionally, blowing of dry air is time consuming. Further, special equipment is required to blow the solvents and the dry air.
One attempt to improve upon the conventional process includes attaching a dust removing film to the top surface of the abrading pad. The purpose of the dust removing film is to confine foreign material, such as fine particles of worn base material and fallen abrasive particles produced by the repetition of the pressing-and-extracting cleaning cycle, so that those foreign materials may not be discharged outside the dust removing film. For example, this process may not be useful for cleaning elastic or springy contact probes (often referred to as xe2x80x9cspring contactsxe2x80x9d or xe2x80x9ccontact springsxe2x80x9d), such as those disclosed in U.S. Pat. No. 6,184,053, entitled xe2x80x9cMethod of Making Microelectronic Spring Contact Elements,xe2x80x9d U.S. Pat. No. 5,476,211, entitled xe2x80x9cMethod for Manufacturing Electrical Contacts, Using a Sacrificial Member,xe2x80x9d U.S. Pat. No. 5,917,707, entitled xe2x80x9cFlexible contact structure with an electrically conductive shell,xe2x80x9d U.S. Pat. No. 6,110,823, entitled xe2x80x9cMethod of modifying the thickness of a plating on a member by creating a temperature gradient on the member, applications for employing such a method, and structures resulting from such a method,xe2x80x9d U.S. Pat. No. 6,255,126, entitled xe2x80x9cLithographic contact elementsxe2x80x9d, and PCT Publication No. WO 00/33089, entitled xe2x80x9cxe2x80x9cLithographic contact elements,xe2x80x9d all of which are incorporated herein by reference.
Another attempt to improve upon the conventional probe cleaning process includes using a polymeric covered wafer to remove foreign materials following the pressing-and-extracting cleaning cycle described above. More specifically, the gel pad is positioned under the probes and then brought into contact with the probes (in a similar manner as the pressing-and-extracting using the abrading pad). The debris that has been loosened by the abrading pad, or produced by the abrading pad, sticks to the gel pad and is thereby removed from the probes. A disadvantage of this cleaning process is that an operator must typically swap the abrading pad with the gel pad during the cleaning process, because testing systems typically include only one auxiliary tray for holding such pads. This is undesirable because it prevents wafer testing from being a completely automated process, thereby significantly reducing wafer testing throughput.
Accordingly, there is a need for improved methods and apparatuses for cleaning probes.
The present invention is directed to apparatuses and methods for cleaning test probes used in a semiconductor testing machine of the type having a plurality of test probes configured to contact the surface of a semiconductor wafer to test one or more dies formed thereon. The test probes being cleaned can be any type of probe, such as tungsten needles, vertical probes, cobra probes, L-type probes, plunger probes, spring probes, contact bump probes formed on a membrane, etc.
In one embodiment, the apparatus of the present invention includes a roller-support arm, and a cylindrical roller supported by the roller-support arm. An outer surface of the roller comprises a sticky material. Debris on the probes will adhere to the sticky material as roller is rolled across tips of the probes.
The roller can comprise an inner cylindrical portion or core, and the sticky material can be disposed on a peripheral surface of the inner cylindrical portion. The roller core spins about its longitudinal axis. Different portions of the sticky material engage against the tips of the probes as the roller core spins. Friction between the sticky material and the tips of the probes causes the roller core to spin as the arm moves in the horizontal direction.
According to an embodiment of the present invention, the roller-support arm is pivotally connected to a wafer chuck of the testing machine. The wafer chuck is typically used for supporting the semiconductor wafer to be tested. An outer circumference of the roller is below a horizontal plane of the wafer when the roller-support arm is in a first position. This enables the wafer chuck to be maneuvered without the roller engaging the probe tips. When the roller-support arm is moved to a second position, at least a portion of the outer circumference of the roller is above the horizontal plane of the wafer and aligned with a horizontal plane of the probe tips. When the arm is in the second position, the outer surface of the roller engages with and rolls across the probes tips as the wafer chuck is moved in a horizontal direction.
According to another embodiment of the present invention, the roller-support arm is connected to some other maneuvering mechanism. That is, in another embodiment, the roller is connected in no way to a wafer chuck.
In another embodiment of the present invention, the roller-support arm extends between a pair of tracks. The sticky material engages the tips of the probes as the arm moves horizontally along the tracks.
In an embodiment of the present invention, the apparatus for cleaning probes also includes a loosening means for loosening debris from the probes. The loosened debris can then be removed using the cylindrical roller having the sticky outer surface. More specifically, the loosened debris will adhere to the sticky outer surface of the roller as it is rolled across tips of the probes.
The loosening means can include a second cylindrical roller having an abrasive outer surface. The debris is loosened from the probes as the outer surface of the second roller is rolled across the tips of the probes.
The loosening means can alternatively include a block having an abrasive top surface. The debris is loosened from the probes as the abrasive top surface of the block is moved in a horizontal direction along the tips of the probes.
In another embodiment the loosening means includes an abrading pad. Debris is loosened from the probes as the abrading pad is repeatedly moved in a vertical direction against and away from the tips of the probes.
In an alternative embodiment, the loosening means includes a second cylindrical roller having a bristled outer surface. Debris is loosened from the probes as the outer surface of the second roller is rolled across the tips of the probes.
In still another embodiment, the loosening means comprises a block having a bristled top surface. Debris is loosened from the probes as the bristled top surface of the block is moved in a horizontal direction along the tips of the probes.
In another embodiment, the apparatus for cleaning of probes includes a roller having an electrostatic outer surface. An arm for supports the roller and engages the roller against tips of the probes. Debris adhering to the tips of the probes is transferred to the electrostatic outer surface of the roller as it is rolled along the tips of the probes.
A method for cleaning test probes, according to an embodiment of the present invention, includes the step of maneuvering a cylindrical roller having a sticky outer surface such that the sticky outer surface is engaged against tips of the probes. The sticky outer surface is then rolled along the tips of the probes to thereby transfer debris adhering to the probes to the sticky outer surface.
Prior to engaging the sticky outer surface of the roller against the tips of the probes, it may be beneficial to first loosen the debris. The debris can be loosened by scraping the tips of the probes against an abrasive surface. This can be accomplished by maneuvering a second cylindrical roller having an abrasive outer surface such that the abrasive outer surface is engaged against the tips of the probes. The abrasive outer surface is then rolled along the tips of the probes to thereby loosen the debris from the probes.
The debris can alternatively be loosened by repeatedly moving an abrasive surface in a vertical direction against and away from the tips of the probes to thereby loosen the debris from the probes.
In another embodiment, the debris is loosened by maneuvering a second cylindrical roller having a bristled outer surface such that the bristled outer surface is engaged against the tips of the probes. The bristled outer surface is then rolled along the tips of the probes to thereby loosen the debris from the probes.
Alternatively, a bristled surface can be moved in a horizontal direction along the tips of the probes to thereby loosen the debris from the probes.
In another embodiment, the method for cleaning test probes includes the step of maneuvering a cylindrical roller having a electrostatic outer surface such that the electrostatic outer surface is engaged or nearly engaged against tips of the probes. The electrostatic outer surface is then rolled along the tips of the probes to thereby transfer debris adhering to the probes to the electrostatic outer surface.
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.